A vertical-cavity surface-emitting laser (VCSEL) is a type of semiconductor laser diode with laser beam emissions perpendicular from the top surface. VCSELs can be mass produced at low cost. For example, tens of thousands of VCSELs can be processed simultaneously on a three inch gallium arsenide (GaAs) wafer.
Optical gyroscopes based on Sagnac effect have no moving parts thus are considered more rugged and less susceptible to interference and damage from acceleration and shock than mechanical gyroscopes. A ring laser gyroscope (RLG) uses a gaseous gain medium in a ring cavity. It is able to support two stable counter-propagating lasing modes due to the Doppler broadening of the gain spectrum where the two counter-propagating modes are supported by different gas molecules separated in the momentum space therefore not competing for energy from the same molecules. Having two counter-propagating beams in the same cavity allows for cancellation of spurious frequency shift caused by minute but unavoidable cavity length changes due to thermal expansion and stress, thus the frequency difference of the two beams only reflects asymmetric effect such as rotation which causes the two counter-propagating beams to experience different cavity lengths. As such, an RLG can achieve extremely high sensitivity to rotation.
The gas laser in an RLG has drawbacks such as gas flow induced interference, leakage from diffusion, and electrode erosion which pose performance and lifetime limitations. Therefore, it is desirable to construct an RIG completely with solid-state components. However, because of the homogeneous broadening in solid-state gain media (no Doppler effect), the two counter-propagating beams compete for energy from the same source, making it extremely difficult to support two stable beams simultaneously.
Alternatively, an interferometric optical gyroscope employs a passive ring cavity or resonator and external light sources to measure the difference in optical length in opposite circular directions as the result of rotation, which can be implemented using free-space or fiber optics, such as interferometric fiber optical gyros (IFOG). The sensitivity of interferometric optical gyros can be enhanced using a high finesse ring resonator. Aside from reducing mirror or fiber losses, adding internal optical gain can be an effective approach to achieving high finesse. However, incorporating a gaseous or solid-state bulk gain medium in the resonator can be complex and problematic due to added scattering, birefringence, thermal, and flow effects. What is needed is a way to introduce optical gain in an optical resonator without these adverse effects.